The present invention relates generally to a forgery-proof code card reader and, more specifically, to code cards of the type that include invisible light and dark codings which are permeable to a selected light band. Although the invention is described in connection with optoelectric code cards, it may be used in connection with other code cards such as magnetic stripe code cards of the like.
There have been known optoelectric code car above type (German Patent Specification No. 27 47 076; German Patent Specification No. 28 43 462) where invisible and/or semi-transparent or slightly transparent reading tracks are provided which are read out by special reading heads each comprising a, preferably, pulse-driven photodiode as a light source and a phototransistor as a receiver, with the card being moved relative thereto. These systems operate preferably with infrared light, if only to improve the protection from forgery, so that such code cards are widely in use in particular as credit cards, check cards, personal identification cards, and the like. It is a common feature of all the optoelectric code card readers known for reading such code cards that the reading tracks and the clock marker tracks, if any, of the code cards are scanned with the card being either moved relative to the reading heads or being stationary, that the data information so obtained, which is offered mostly serially, but sometimes also serially in parallel bit packets, is then evaluated whereupon access to a building is provided, a certain activity is authorized, for example the payment of a certain amount of money, or --to say it in more general terms--a generally permitted manipulation on the part of the carrier of the card is no longer hindered.
A particular problem of these code cards lies in the difficulty of protecting them from forgery, since it must of course be ensured that any abuse of such code cards is excluded.
Although it has been known in this connection to provide certain cards, for example credit cards, with a magnetic track on their reverse side containing certain data information, this provides, however, the problem that the magnetic track may get lost if it gets into contact with strong static magnetic sources, or that it may be detected by corresponding measuring instruments if the card gets into the hands of an unauthorized person, if only for a short time.
In the case of another known device (German Disclosure Document No. 25 59 430) it is part of the checking procedure of such identity documents that during the reading process at least one photodiode operates also in pulse operation, with the light sources switched on. This is necessary for safety reasons because this pulse operation permits an additional phenomenon to be utilized as a recognition aid. The latter consists in compounds of special earths being arranged in the code card itself as special check substances which offer the particularity that pulsating light impinging upon them is reflected or permitted to pass with a given time lag. A properly time-adjusted pulse oscillator then permits to utilize these time lags as an additional identification feature. However, it is necessary for this purpose that the code card be at rest, i.e. static, during reading. If in the case of the reading principle just described reading were effected dynamically, i.e. with the card moving, then the card would have to be moved through the feeding channel at a precise speed because otherwise it would be impossible to tune the system to the time lag of the light pulses specific for the given check substances. On the other hand, if the reading operation were carried out statically, the code card would have to be positioned precisely in the reading channel which would require high production precision, not only as regards the guide elements in the channel, but also as regards the dimensions of the card. And this would also mean that the card would have to be kept free from any external mechanical deformation and damage and that a damaged card would no longer be acceptable in use.
The described known checking principle is complicated, it requires the arrangement of specific compounds in the card, which is rather troublesome, and it is in addition dependent on certain external, reproducible reading conditions which must be produced with a corresponding accuracy. Further, it is a requirement of this known checking principle that the card must be clear-transparent at the point where the so-called check substance is arranged, that only light of a given wave length is used, which is not always guaranteed by aging photodiodes, and that at least the point where the check substance is arranged must always be kept clean because otherwise reading errors are unavoidable.
Now, it is the object of the present invention to make an optoelectric code card reader and the associated code card highly forgery-proof, without great input, by detecting special properties of the code card related to its light-permeability with the aid of special, properly tuned sensors arranged in the area of the reader and verifying in this manner the general permissibility of the card.